Atlanta — A Detroit jury drew a line on the controversial home-defense “castle doctrine” Thursday, finding Theodore Wafer of Dearborn Heights guilty of second-degree murder in the shooting death of Renisha McBride, an unarmed black teenager seeking help at his door after a car accident.

The seven-man, five-woman jury took less than a day to find Wafer guilty after a 10-day trial ended Wednesday. Sentencing is scheduled for Aug. 21.

Prosecutors said Wafer was itching for a confrontation when he opened his door in the early morning hours after an intoxicated Ms. McBride, who had been in a nearby car accident, beat so hard on the door that the coroner found her hands swollen.

Wafer, taking the stand in his own defense, agreed that he was full of “piss and vinegar” over the loud noise, but only because, as he said, “I didn’t want to cower.… I didn’t want to be a victim in my own house.” He said he fired out of fear for his life. According to testimony, no words were exchanged between the two.

Despite racial tension over the case – in a city that’s 80 percent black, Wafer was a middle-aged white man and McBride a black teenager – the subject didn’t come up in the trial. Wafer told jurors that he didn’t know McBride’s gender or race until after he had shot her through a locked screen door.

The case threw a spotlight on crime tensions in Detroit, a city with the highest rates of justifiable homicide in the US. Many of those homicides include homeowners defending their homes against intruders.

Michigan, as with most states, protects homeowners from liability in cases of legitimate self-defense, as long as they meet a standard: that they respond with deadly force only after “honestly and reasonably” believing they were in imminent danger.

The verdict also became another milestone in America’s larger debate over liberalized gun rights and self-defense laws, some of which critics, including the prosecutor in this case, have said can create a “shoot first, ask questions later” dynamic that can lead to the death of innocent people.

"We have gun issues in this country and people are shooting other people, and some of them are doing it purposely and some of them are doing it accidentally, but some of them are just doing it based upon wrong impressions,” says New York City attorney Barry Slotnick, whose successful defense of “subway vigilante” Bernhard Goetz in 1984 hinged on changing attitudes toward armed self-defense in America.

“If a [defendant] says, ‘It was 4 in the morning, I heard banging, people were trying to break into my house and come kill me, so I shot them first’ – if a jury believes that’s what that person believed, he gets acquitted.”

At least according to the jury in the Wafer trial, the homeowner in this case failed to meet the standard of justifiable use of deadly force.

During the trial, Wafer’s attorney, Cheryl Carpenter, told jurors that McBride’s pounding on Wafer’s home caused walls to shake and pushed windows to the breaking point. Prosecutor Patrick Muscat countered that Wafer treated the weapon “like a toy” and came to his front door “want[ing] a confrontation.”

Commentators noted several problems with Wafer’s defense, including the fact that he first told police that the shooting was an accident, only later changing it to self-defense. At one point during the trial, he even conceded to prosecutors that, “I should’ve called [the police] first.”

Mr. Slotnick says the defense made a major error in putting Wafer on the stand, noting that if George Zimmerman – who was acquitted last year in the Trayvon Martin shooting, also involving an unarmed black teenager being killed by a zealous gun carrier – “he would’ve been toast.”

The verdict was cathartic for at least some in the strife-ridden city, where Detroit Free Press columnist Brian Dickerson noted that Wafer’s “suburban home straddles a shifting demographic fault line where whites, blacks, and immigrants from three continents share working-class challenges and a sense of post-industrial anomie.”